2
3/20/2003CVEN 349 - Maxwell 2 Purpose: Introduce the ideas that: Construction is a variable process. – there are few constants. These variations cause risk in estimating any outcome. And There are ways to deal with that risk.

4
3/20/2003CVEN 349 - Maxwell 4 PERT – Basic Concept First used by NASA to Flow-Chart and Schedule their projects. Approach is used for projects where the activity durations and costs are largely guess work – that is, SWAGs. Works surprising well on large projects because of the math and statistics.

9
3/20/2003CVEN 349 - Maxwell 9 Central Limit Theorem Given N samples of size M drawn from the same population of unknown distribution. The Mean of the distribution of the sample means (DSM) is an unbiased estimator of the population mean. The Variance of the DSM is an unbiased estimator of the Variance of the population divided by the sample size M. Standard Deviation = SQRT of the Variance The DSM approaches normal as M approaches infinity. M = 30 is generally OK.

10
3/20/2003CVEN 349 - Maxwell 10 The Problem is the Shape of the Curve – What Distribution? We assume Normal for ease of use but the tails are too thin causing an underestimation of extreme cases. A Triangular is easier to use but the tails are too fat causing over- estimation of extreme cases. A gamma distribution appears a best fit to most unsymmetrical cases.

15
3/20/2003CVEN 349 - Maxwell 15 Class Exercise Stay in your seat. Independently, Guess at the length of the class room and write it down on a piece of paper. As Tables of (3 or 4), write down your best guess for the: Lo, ML, Hi Report them to me by groups of 4 (teams).